The present invention relates, in general, to a photonics package incorporating a monolithically integrated alignment device for coupling optical energy between in-plane optical devices and to a method for producing the same. More specifically, the invention relates to a photonics package that incorporates an optical coupling and alignment device having an integral fiber groove, lens aperture and monolithic aspheric lens.
Data in optical communication systems is often transmitted in the form of optical signals through an optical fiber terminating in a photonics device such as a receiver, transponder, transceiver, or the like. The data is projected from an optical fiber, for example as a light beam, directed onto a photonic die where the data is received by a photodetector and converted to a corresponding radio frequency (RF) electrical signal. However, data can easily be lost due to improper alignment between the fiber and the photodetector or through light divergence, although both the alignment and divergence problems can be minimized where the fiber and the photodetector are in close proximity or where a lens can be used to focus the optical signal. In general, these optical coupling systems are increasingly prevalent so that the need for simplified assembly processes for micro-optical coupling systems is increasingly important.
There are presently two broad approaches to photonics packaging. In the first, an optical fiber is aligned to be perpendicular to a photodetector; in the second, the fiber is in-plane (i.e. parallel) to the photodetector. In the first construction, wherein light is projected from fiber directly onto the photodetector, the photodetector and the fiber must be optically aligned in three mutually perpendicular planes ((x-y), (x-z), and (y-z)), which complicates the assembly process. Moreover, such an arrangement can be problematic for high frequency data transfer because it requires a longer wire bonding or transmission line, and this reduces device performance at high frequency operation. This design configuration also results in the optical input being perpendicular to the RF signal output, and this requires much more space in a module. These performance and size issues make this approach commercially less desirable, and this is the disfavored, if not unacceptable, approach for many applications where it is advantageous to have the fiber input and RF output substantially coplanar.
In the second construction, where the fiber is parallel to the photodetector surface, the optical signal from the fiber must be redirected in order to impinge on the photodetector. One known method for redirecting the optical signal in this type of alignment device is to reflect the optical signal off a mirror in a direction perpendicular to the axis of the fiber. However, there are several problems with this method. Using a discrete mirror (an additional element needing alignment) introduces an indirect connection between the fiber and photodetector, causing difficulty during alignment, raising costs due to the need for a more precise construction, and reducing reliability. Further, in order to accurately direct the optical signal onto the mirror, and then to the photodetector, the optical fiber holder has to incorporate a lens. Therefore, there are certain commercial advantages to eliminating the intermediate mirror.
Another method for redirecting an optical signal from an optical fiber onto the surface of a plane perpendicular to the axis of the fiber involves cutting the terminal end of the fiber at an angle so that the signal in the fiber is deflected out in a direction approximately perpendicular to the axis. The fiber is then positioned so that the signal exiting the fiber passes through a lens, in order to align and focus the signal. This design is an improvement over prior devices, but since high frequency optical signals require miniscule photodetectors, the optical fiber must be in extremely close proximity to the photodetector to minimize light divergence and to maximize photodetector responsivity. Further, the three components; namely, the fiber, lens, and photodetector, have to be precisely located with respect to each other to ensure reliable coupling, and this is difficult to accomplish.
In each of the configurations discussed above, the photonic package consists of several independently fabricated micro-optical components, including an optical fiber, a photodetector, a mirror, a lens and and a substrate or microbench on which the components are assembled, as well as bonding materials to connect the components, and frequently all were assembled manually, which is not efficient. Although automated assembly could be used, it fails to achieve the needed alignment precision. Accordingly, a simple construction for optically aligning a photodetector in a parallel orientation with an optical fiber is needed.